Neutralized amplifier circuit



Nov. 19, '1940.

E. RAHN ET AL 2,222,423

NEUTRALIZED AMPLIFIER CIRCUIT Filed Aug. 10, 1959 INVENTORS ERNST RAHN ERW/N W/L ACHER ATTORNEY.

.Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE NEUTRALIZED AMPLIFIER CIRCUIT Application August 10, 1939, Serial No. 289,420 In Germany July 6, 1938 4 Claims.

'I"ne invention is concerned with a neutralized amplifier circuit scheme especially suited for ultra-short waves. This circuit arrangement offers the advantage over others known in the 5 prior art that in the presence of unvaried neutralization, that is to say, with perfect freedom from reaction between output circuit and input circuit, it is possible to bring about in a controlled manner either de-attenuation (regenerlO ation) or damping in the amplifier tube. This provides ways and means for insuring far higher amplification or a substantially better stabilization of the circuits together with an avoidance of stray .or interfering oscillations.

15 Neutralization, that is, freedom from reaction between input and output circuit of a tube arrangement is practiced as a general rule by the aid of bridge schemes. However, such bridge schemes do not always insure freedom from feedback, that is to say, freedom from reactions produced by the plate circuit upon the grid filament path or circuit. Now, the object of the invention is to act upon the feed back under proper conditions of measured control or regu- 95 lation so that, as a result, the circuit organization may be either regenerated or damped to a desired degree, while neutralization as hereinbefore defined will be fully preserved.

7) Two tubes are used according to the invention of which one, if desired, is not heated or replaced by an impedance simulation. The plates of these tubes are inter-connected directly and the grids by way of the input circuit, while, .on

M the one hand, between the cathodes, and, on the other hand a shiftable tap of an impedance (inductance) connected between the point of symmetry of the input circuit and the plates variable impedances (cathode circuits) are connected.

It has already been suggested in the prior art of frequency doubler circuit schemes, that is to say, in circuit organizations comprising two tubes the plates of which are connected with each other, while the grids thereof are excited 45 in push pull to introduce cathode circuits, that is, tunable circuits between the cathodes and ground. However, it has been discovered that neutralization, to be sure, in the sense as above defined, is preserved, but that the feedback can- 50 not be acted upon to an adequate degree even by making the cathode circuit variable. Contradistinct to this scheme, the cathode circuits are not inserted between the cathode and the ground, but between the cathodes and a variable interme- 55 diate point of the output circuit.

(Cl. 179-471) r Figures 1, 2 and 3 show neutralized amplifiers in accordance with the invention.

Figure 1A shows the equivalent circuit of Fi ure 1.

The invention shall now be explained in more I detail by reference to the accompanying draw-. ing. Fig. 1 shows a frequency doubler circuit organization comprising the heated tubes l and 2, the input circuit 3, the output circuit 4 and the cathode circuits 5 and 5'. These cathode circults consist preferably of tunable Lecher-Wire lines. According to the invention, the junction point of the two cathode circuits is joined with a variable tap of the output coil 4. The bridge scheme corresponding to Fig. 1 is represented in Fig. 1a, where G! and G2 the points where the grids are in the two tubes; E is the grounding terminal and A the anode terminal. The rest of the reference numerals are the same as in Fig. 1. It will be noted that the output circuit and the input circuit are perfectly neutralized or balanced out in reference to each other, in fact, the decoupling is independent also of the terminal where the cathode circuit 5 and the output coil 4 join. Now, while properly preserving neutralization, it is now feasible by shifting the said tap to adjust conditions so that any desired regeneration or damping is obtained.

Regeneration (or de-attenuation) is particularly favorable since it applies to the doubled frequency, with the result that the whole circuit scheme is regenerated for the useful or signal frequency while its properties are unaltered for the fundamental. The operation of the variable connection of the cathode circuit with the output circuit is predicated upon the fact that a grid alternating potential regulable both as to size and phase is produced, it being advantageous not only to shift the slider or tap, but also to tune the cathode circuit.

The circuit organization as shown in Fig. 1 operates with two distinct cathode circuits 5 and 5, though as shown in Fig. 2 the same could be replaced also by a single cathode circuit 5. In this instance, however, the cathodes must be connected by way of an impedance, with the cathode circuit being connected with an intermediate point or tap of this impedance as can be seen also from Fig. 2.

The bridge scheme which corresponds to Fig.

2 results directly from the bridge scheme Fig. 1a. so that there is no particular need for a detailed description thereof. What may be emphasized, however, is that for the purpose of prebalance.

serving the state of neutralization, of course, the bridge formed by the points marked GI, G2, Kl, K2, must be in state of balance. As a consequence, the position of the variable tap on the coil 4 will remain entirely without efiect upon the neutralization.

The fact that it is possible to practice regeneration in the circuit organization is extremely important in connection with the use of decimeter waves inasmuch as these can be amplified to a marked degree only where the de-attenuation is marked.

If in the circuit organizations shown in Fig.

1 or Fig. Z'tube 2 is not heated or if the same is replaced by a tube simulation, then, while the circuit arrangement remains otherwise the same, the identical effect is obtainable as with a heated tube. All that happens is that the "frequency doubler action is absent, in fact, that amplification at a frequency of 1:1 is produced. Also in this case where a neutralized one-tube circuit scheme is concerned, it is advantageous to insure controllable regeneration or damping, while neutralization is preserved. .If, finally, the tube simulation consists of inductances rather than capacitances, so that merely the impedance ratio of the various impedances occurring in the tube is simulated, there results a circuit arrangement of the kind shown in Fig. 3 which, for reduced wave bands offers particularly great advantages because of its simplicity. This circuit arrangement distinguishes itself merely from the other schemes insofar as the output circuit is not constituted by the inductance 4, but by the inductance 2 which is split at the ratio of the tube capacity reactances, that is, the part above the tap is to the part below as Cpg is to Cgk. The circuit for putting out or taking off the useful or signal energy is designated by 6 in Fig. 3. The input circuit 3 is situated between the grid and the point of symmetry of inductance 2. Also, this circuit organization really represents a balanced bridge in which adjustment of the feedback is feasible without essentially afiecting the bridge It willbe understood, however, that this circuit organization is not perfectly independent of the wavelength since the bridge comprises both capacities and inductances. However, for reduced wavebands this disadvantage may be readily tolerated.

Attention may finally be drawn to the fact that the circuit schemes here shown and discussed represent merely the underlying principle of the .circuit arrangements, for all direct current circuits, biasing potentials, etc. have been omitted,

in fact, only such RF circuits have been included as are essential for operation. Neither is the invention restricted to the exemplified embodiments here shown, for there are conceivable a number of equivalent solutions most of them based upon an exchange or transposition of the electrodes of the tubes. For instance, it is possible to exchange the terminals of the grid and the anode or plate so that what was before the input circuit would then play the part of the output circuit, and vice versa. However, there is no need to enter into these additional possibilities of applying the basic idea of the invention for they are really nothing else but a logical development of what has been disclosed above.

We claim:

1. A neutralized amplifier circuit for ultrashort Waves comprising a pair of tubes each having a cathode, a grid and an anode, an input circuit connected between the grids of said tubes, a direct connection between the anodes, an output impedance connected between said direct anode connection and the input circuit, an impedance connected between the cathodes, an adjustable tap on said output impedance, and a connection from an intermediate point on said cathode impedance to said adjustable tap.

2. A neutralized amplifier circuit as defined in claim 1 wherein the last-mentioned connection includes a variable impedance.

3. A neutralized amplifier circuit for ultrashort waves comprising a pairof tubes each having a cathode, a grid and an anode, an input circuit connected between the grids of said tubes, a

direct connection between the anodes, an output impedance connected between said direct anode connection and the input circuit, an adjustable tap on said output impedance, and a variable impedance connected between each of the oathodes and said adjustable tap;

4. A neutralized amplifier circuit for ultrashort waves comprising a pair of tubes each having a cathode, a grid and an anode, a tunable input circuit connected between the grids of said tubes, a direct connection between the anodes, an output impedance having one end connected to said direct anode connection and the other end to a point of symmetry of the input circuit, a variable impedance connected to each of the cathodes, and a connection from the junction point of the two cathode impedances to an adjustable tap on the output impedance, said adjustable tap controlling the degree of regeneration.

ERNST RAHN. ERWIN WILLWACHER. 

